Common Interface

In Digital Video Broadcasting, the Common Interface is a technology which allows separation of conditional access functionality from a digital TV receiver-decoder (Host) into a removable conditional-access module (CAM). It is also referenced as DVB-CI for Digital Video Broadcast - Common Interface. The host is responsible for tuning to pay TV channels and demodulation of the RF signal, while CAM is responsible for CA descrambling. The Common Interface allows them to communicate with each other.

The Common Interface can be used for pay-to-view TV ; a module is used to interface between the pay-to-view card and the TV or device. This allows manufacturers to install a single (common) interface into their devices rather than many. It is a similar concept to USB.

All Common Interface equipment must comply with the EN 50221-1997 standard. This is a defined standard that enables the addition of a conditional-access module (CAM) in a DTV receiver to adapt it to different kinds of cryptography. Indeed, one of Digital Video Broadcasting's main strengths is the option of implementing the required conditional access capability on the Common Interface.

This allows broadcasters to use modules containing solutions from different suppliers in the same broadcast system, thus increasing their choice of anti-piracy options.

The interconnect is formed between a host and a module. Examples of a host are a digital television or digital set-top box. The EN 50221 specification allows many types of module but only the conditional-access module (CAM) has found popularity because of the pay TV market.

A DVB receiver may have one or two slots implementing the Common Interface (CI). The CI uses the conditional-access module (PCMCIA) connector and conforms to the Common Scrambling Algorithm (CSA), the normative that specifies that such a receiver must be able to accept DES (Data Encryption Standard) keys in intervals of some milliseconds, and use them to decode private channels according to a specific algorithm.

...
Wikipedia